The development of a fiber optics pressure catheter is proposed for NHLBI Subject 56.D. The optical pressure sensor using elasto-optics material is much smaller in diameter (less invasive) than the currently used electronic pressure catheter. It is inserted into blood vessels (arteries, veins or heart chamber) and capable of measuring blood pressures (O to 300 mmHg) with a very high accuracy (better than 3 mmHg). The sensor is bio-compatible and causes no medical problems. The sensor is also stable over long time periods (72 hrs) and for temperature changes (30 to 50 degrees centigrade). The manufacturing cost of the sensor head would be very inexpensive (less than $100) so that the head can be disposable. The sensor will help monitor heart conditions after open heart surgery. Because of its small size it can be used for the young. The primary commercial application of this device will be in cardiology. It can also be used to monitor fluid pressures in the human brain after surgery. The Phase I effort will demonstrate the feasibility of the proposed approach while full product development is for Phase II.